<form id="form">
    <p v-repeat="items">
        <input type="text" name="text{{$index}}" v-model="text">
    </p>
    <button v-on="click: add" id="add">Add</button>
    <p id="texts">{{texts}}</p>
</form>

<script src="../../../dist/vue.js"></script>
<script>
    var app = new Vue({
        el: '#form',
        data: {
            items: [
                { text: "a" },
                { text: "b" }
            ]
        },
        methods: {
            add: function(e) {
                this.items.push({ text: "c" })
                e.preventDefault()
            }
        },
        computed: {
            texts: function () {
                return this.items.map(function(item) {
                    return item.text
                }).join(",")
            }
        }
    })
</script>